In the past, nitrile rubber (acrylonitrile-butadiene copolymer rubber) has been used as a material for rubber parts for automobile such as hoses, belts, and tubes by making use of its oil resistance, mechanical properties, chemical resistance, etc. Further, highly saturated nitrile rubber obtained by saturation of carbon-carbon double bonds in the polymer main chain of nitrile rubber by hydrogenation etc. is further excellent in heat resistance and is being used for rubber parts such as seals, belts, hoses, and gaskets.
For example, Patent Document 1 discloses a nitrile group-containing highly saturated copolymer rubber comprising α,β-ethylenically unsaturated nitrile monomer units (a) and conjugated diene monomer units (b) and having at least part of the conjugated diene monomer units (b) hydrogenated, where a ratio of content of α,β-ethylenically unsaturated nitrile monomer units (a) is 37 to 45 wt %, a total of the α,β-ethylenically unsaturated nitrile monomer units (a) and the conjugated diene monomer units (b) is 93 wt % or more, an iodine value is 9 or less, and a half value width of a peak of a loss tangent tan δ in a viscoelastic property in the case cross-linked is 5 to 20° C. in range.
However, the cross-linked rubber obtained by using the nitrile group-containing highly saturated copolymer rubber of the above Patent Document 1 is insufficient in tensile stress and therefore is not suitable for applications such as belt applications in which particular excellence in tensile stress is demanded.